Field of the Invention
The present invention relates to a process for producing a relief pattern in a thin plastic card such as a bank card.
Description of the Related Art
In the field of plastic cards, it is known to produce rigid thin plastic cards by joining layers of polyvinyl chloride (PVC) or polycarbonate (PC).
It is known to produce such thin plastic cards, in various formats, so as to obtain portable cards. These cards may be equipped with a unit for storing information, a unit for processing information (microcircuit) or even be able to communicate with an external electronic or information-processing device via a contact or contactless means of communication.
These cards are characterized by a substantially planar shape limited by centimeter-sized dimensions and by a thickness that is most often smaller than 1 mm, such as defined by the standard ISO 7816.
Such thin plastic cards are used as bank cards, identity cards, medical cards, badges, phone cards, etc.
Many reasons may be used to justify the need to produce at least one relief pattern in such a thin plastic card. A relief element enables differentiation in that a card containing a relief is easier to locate, both by eye and by touch. A relief makes it possible, for example by means of Braille inter alia, for a visually impaired or blind person to identify the card. The presence of a relief may even allow an imprint to be taken. This has, for example, for a long while been used to record the details of a debtor during a bank payment, a bank card belonging to said debtor and comprising said details in relief being pressed against a pressure sensitive receipt, such as carbon paper receipt. A relief also allows a security level 1 device (i.e. a security device that does not require a tool for verification) to be added to a thin plastic card.
A plurality of methods are already known allowing a relief pattern to be produced in such thin plastic cards.
According to a first method, a relief pattern is produced by depositing a lacquer on a thin plastic card. This method is implemented by screen printing. The result obtained is limited to very small thicknesses, the relief not exceeding 100 μm relative to the external surface of the thin plastic card.
According to another method, a relief pattern is produced by depositing ink on a thin plastic card. This method is implemented by inkjet printing, also referred to as drop-on-demand printing. The result obtained is limited to very small thicknesses, the relief not exceeding 100 μm relative to the external surface of the thin plastic card.
According to another method, a relief pattern is produced by carbonizing a surface layer (for example made of polycarbonate) of a thin plastic card. This method is typically implemented by means of a laser, typically at a wavelength of 1064 nm. The relief thus obtained is hardly any higher, not exceeding 140 μm relative to the external surface of the thin plastic card.
According to another method, called embossing, a relief is obtained mechanically by means of a stamp applied to one side of a thin plastic card so as to push out material and cause, by deformation, a positive relief to appear on the other side. This method is typically implemented by means of a system comprising at least one stamp paired with a die. The relief thus obtained is clearly much higher than that obtained with the other methods described above, and may reach 400 to 500 μm relative to the external surface of the thin plastic card. However, this method has at least two drawbacks relating to the use of stamps. A first drawback is to limit the choice of possible patterns to a given set of stamps/dies. Such a method is thus typically limited to a given set of characters, in a given typeface, for which stamps exist. In the absence thereof, for any other pattern, it is advisable to develop a suitable stamp/die. A second drawback is that penetration of the stamp causes a negative of the same relief to appear on the side opposite the positive relief. This negative relief makes the surface opposite a relief pattern unusable or hardly usable. Thus a printing in such a zone will become unreadable or hardly readable once impressed by the stamp.